The invention relates to an optical system of colposcope and more particularly, to such an optical system of colposcope including an illumination, an observation and a photographing optical sub-system.
Recently the effectiveness of the colposcopy is recognized in detecting uterocervical cancer in the early stage thereof, and there is a need for a colposcope having an excellent performance. FIG. 1 shows the optical system of a conventional colposcope which includes independent observation optical sub-system 1 and photographing optical sub-system 2. A magnification varying optical sub-system 5 is contained only in the observation sub-system 1. Hence, if the magnification in the sub-system 1 is changed, the magnification in the photographing sub-system 2 remains unchanged, disadvantageously resulting in the lack of coincidence between the extent of observation field and the field being photographed.
The observation optical sub-system 1 includes an objective 4, a magnification varying sub-system 5, Porro prism 6 which converts an inverted image into an erect image, and an eyepiece 7. This constitutes an independent optical sub-system which permits an observation of an object being examined (not shown) which is illuminated by an illumination lamp 13 through an illumination optical sub-system 3. The illumination optical sub-system 3 includes a lens 14 which focusses light from the lamp 13, a pair of prisms 15, 16 which are used to divert the optical path, and a condenser lens 17. The photographing sub-system 2 is also an independent optical sub-system including a prism 10 which diverts the optical path for reflective light from the object being examined, lens 8, reflecting mirror 11 and focussing lens 9, which focusses a light image of the object onto a photographic film 12 which is located at a given position.
As mentioned previously, when the magnification of the observation sub-system 1 is changed, the extent of the picture taken or picture frame does not coincide with the extent of the field observed. In order to avoid this drawback, there has been proposed another optical system as shown in FIG. 2. In the arrangement of FIG. 2, the object being examined is again illuminated by the lamp 13 through the illumination sub-system 3, and the light from the illuminated object is passed through an objective 24 and through a magnification varying optical sub-system 25 and is then split into two optical paths each associated with an observation sub-system 21 and a photographing sub-system 20. Light incident into the photographing system 20 is focussed by a focussing lens 19 onto the light sensitive surface of the film 12. Light impinging on the observation sub-system 21 is passed through a lens 23 and through Porro prism 6 and eyepiece 7 to reach the eye. With this arrangement, the overall optical system is of a single lens reflex type where the magnification varying sub-system 25 is common to both the observation and the photographing sub-system 21, 20, thus achieving a coincidence between the extent of the field between the observation and photographing sub-systems.
However, the described optical system includes the beam splitter 22 which divides the incident light into two optical paths, thereby tending to cause a substantial reduction in the amount of light fed into both sub-systems 20, 21. As a result, the field of these sub-systems may be darkened. This difficulty may be eliminated by an increased aperture of the optical system, which however disadvantageously results in a larger and more complex arrangement.